Extraction process for separating a hydrocarbon from a mixture thereof employing pyridine oxide or alkylpyridine oxide



ilnited States Patent Cfiice 2,850,547 Patentedsept. 2, 1958 EXTRACTIONPRO'JE FUR SEPARATING A HYDROCARBON FROM A MIXTURE TEERE'GF EMPLQYEJGPYRIDINE OXIDE R ALKYLPYRIDM OXIDE Paul N. Rylander, Chicago, Ill.,assignor to Standard 0i! Company, Chicago, EL, a corporation of IndianaN0 Drawing. Application March 9, 1955 Serial No. 493,305

8 Claims. (Cl. 260674) duced as processed or unprocessed petroleum oilsor mineral oils, oil fractions containing neutral organic oxygencompounds (derived from the Fischer-Tropsch and similar syntheses), coaltar oils, shale oils and the like. Various aromatic hydrocarbons are ofvalue as solvents and for the preparation of resins, plasticizers andvarious other chemical derivatives; in addition, their removal fromvarious hydrocarbon stocks containing the same may be desired in orderto prepare partially dearomatized hydrocarbon stocks for thermal orcatalytic cracking, for hydrogenation operations, for use as heater oilsand for other purposes.

With the commercial development of new processes for producing aromatichydrocarbons boiling within the gasoline boiling range bycyclization-dehydrogenation of parafiinic hydrocarbons and by thedehydrogenation of cycloalkanes there has come an increased demand forprocesses to separate and concentrate the aromatic hydrocarbons thusproduced. Thus, with the commercial development of such processes ashydrofo-rming, platinum catalyst reforming of naphthas, and the like, atremendous potential has been created for the production ofnitrationgrade aromatics such as benzene, toluene and xylenes forv useby both the petroleum and chemical industries.

It is an object of my invention to provide a process for the selectiveextraction of hydrocarbon mixtures with specified novel solvents.Another object of my invention is to provide the art of selectiveextraction of hydrocarbon mixtures with novel solvents, viz. pyridineoxide and alkylpyridine oxides. A further object of my invention is toprovide for the employment of new solvents in a process for theselective extraction of aromatic hydrocarbons from homogeneous liquidmixtures thereof with aliphatic hydrocarbons, particularly saturatedhydrocarbons. A further object is to provide processes for theconcentration and purification of aromatic hydrocarbons, particularlythose containing not more than about 19 carbon atoms per molecule. Anadditional object is to provide a process for the selective extractionof aromatic hydrocarbons from mixtures thereof with clefinichydrocarbons. Yet another object is to provide a process for theselective extraction of olefinic hydrocarbons from saturatedhydrocarbons. Other objects are to provide processes for the selectiveextraction of isoparafiinic and cycloparafiinic hydrocarbons from thenormal parafiins. One more object is to provide a process for theselective extraction of cyclic olefins from acyclic olefins, forexample, the selective extraction of cyclohexene from mixtures thereofwith n-hexene. A further object of this invention is to provide aprocess for the separation of close-boiling or azeotropic mixtures ofaromatic hydrocarbons with saturated hydrocarbons by extraction orextractive distillation with pyridine oxide or alkylpyridine oxides.Another object is to provide a process for refining hydrocarbon oils byextraction with novel solvents. These and other objects of my inventionwill become apparent from the ensuing description thereof.

Pyridine oxide has the structural formula and alkylpyridine oxidescontain nuclear C-alkyl groups, e. g. as in the N-oxides, derived fromthe picolines, lutidines, collidines, methylethylpyridines (especiallyZ-methyl-S-ethylpyridine), propylpyridines, butylpyridines and otherhomologs of pyridine.

Pyridine oxide and alkylpyridine oxides supercool readily and can beobtained and employed in selective extraction as liquid materials attemperatures well below the melting points of the pure compounds, due tosupercool-.

ing, the presence of extracted hydrocarbons in the solvents an-d, ifdesired, by the addition of auxiliary solvents which can be employed tolower the melting point of the pure solvents substantially. The oil tobe extracted can be mixed with solid pyridine oxide, which selectivelyabsorbs the most polar constituents of the feed and liquefies in theprocess to produce a distinct extract phase.

Under otherwise constant operating conditions (temperature, ratio ofsolvent to feed, extraction temperature,

molecular Weight of the feed stock, etc.) the solvent power of my novelsolvents increases through the series: normal paraflins, isoparafiins,cycloparafiins, acyclic olefins, non-conjugated diolefins, cyclicolefins, conjugated diolefins, aromatics and aromatics containingunsaturated substituents. In general, hydrocarbons of mixed type, forexample, alkyl aromatics, are absorbed in the solvents of this inventionto a degree intermediate to the degree of solution of the pure structurecomponents (unsubstituted aromatics and parafiins) v In general,extraction operations can be conducted at temperatures between about 0C. and about 150 C., more or less, depending upon the particularcharging stock, the particular solvent or solvents, the solventzfeedratio, the number of extraction stages, the degree of extraction whichis sought, the proportions of auxiliary solvents (if any), etc., as willbe apparent to one skilled in the art. temperatures between about 30 C.and about 150 C. and in the extraction of naphtha boiling range stocks,I prefer to employ temperatures between about 40 C. and about C.Generally, the selection of a suitable extraction temperature is notcritical.

The ratio of solvent to hydrocarbon feed stock, in liquid extractions,must be suificient to exceed its solubility under the extractionconditions in said feed stock in order to form two distinct liquidphases, viz. a rafiinate phase containing little or no solvent and animmiscible extract phase comprising the amine oxide and extractedhydrocarbons. Generally, I may employ between about 0.5 and about 50volumes of solvent per volume of hydrocarbon charging stock. Ordinarily,I prefer to employ between about 1 and about 20 volumes of solvent per.volume of feedstock, especially in the treatment of naphtha boilingrange stocks (about Sufiicient pressure is maintained within theextraction zone to prevent substantial volatilization of the hydrocarboncharging stock or solvent under the liquid-liquid extrac- Usuallyliquid-liquid extraction is effected at.

400 F. end-point)..

- for other reasons.

tion conditions. It isobvious that pressure and tempera given case. canbe determined readily by experiment.

. Any means of separating extracted materials from the be employed. Thusunder certain conditions, it may be desirable to distillextracted-materials from a relatively lnvolatile solvent or to wash themout of the extract layer with-,a paraflin hydrocarbonhaving a differentboiling point. Also, the amine oxide solvents may in some instances berecovered from the extract layer by crystallization or washing with asolvent which is highly selec- ,tive therefor, such as cold water,acetone, ethers, etc.

The amine oxide solvents :hydrate readily, but they can easilybedehydrated, e. g. by azeotropic distillation with benzene, andreturned for use in the extraction process.

It maybe desirable toemploy diluents or auxiliary solvents-in specificcases in order to modify solvent selectivity, to lower solvent meltingpoint (thereby permitting extraction to be effected at relatively lowtemperatures, e; g., well below the melting point of the solvent) or Theamount of auxiliary solvent can be .selected with reference to specificcases; ordinarily, between about 1 and about 20 weight percent or evenmore, based on theprincipal solvent, may be employed. The auxiliarysolventshould be miscible tothe desired extent with the principalsolvent, and should preferably be a neutral compound. As examplesofauxiliary solvents which may be employed, one may mention the sulfolane s, for example, 2,4-dimethylsulfolane, 2,3-dimethylsulfolane and thelike; various nitriles such as acetonitrile, .bis-2-cyanoethyl ether andthe like; various 'ethers suchas diethyl ether, methyl-tert-butyl ether;glycols or their ethers having the structure R O(CH CH O),,R and (IJHQBlown-brownie wherein R ,and R are hydrogen or alkyl groups and n ethylcarbonate, bis-Z- hydroxyethyl carbonate, bis 2-.

chloroethyl carbonate, bis 2 methoxyethyl carbonate,

ethylene carbonate, n-butyl formate, methyl furoate, di-,

methyl oxalate, diethyl succinate, dimethyl phthalate,dimethylisophthalate, and the like; neutral organic nitrogen compoundssuch as N,N-dialkyl formamides (particularly dimethyl 'formamide),dimethyl hydantoin and the like, nitro aromatics such as nitrobenzeneand the like; ketones, for example, acetone, methyl ethyl ketone, methylisoextract phase and of recovering solvent therefrom may troleum, coal,shale, etc., are known to contain aromatic hydrocarbons and organicsulfur compounds whose removal is sought in order to produce refinedhydrocarbon oils. Such oils may boil within the boiling range of (andthe oils may be generally characterized as) gasoline or naphtha, crackednaphthas, coke still naphthas, kerosene, virgin gas oil, cracked gasoil, hydroformer bottoms, heater oil, furnace oil, diesel fuel,transformer oil, crude oil, reduced crude oil, vis-brokencrude oil,lubricating oil distillates, etc.

The present process may also be applied to the refining of various coaltar fractions and coal tar distillates, or of neutralizedFischer-Tropsch process fractions. In the refining of oil fractions thepresent refining agents serve not only to effect selective extraction ofaromatic hydrocarbons (and olefins, to some extent) but also to removebutyl ketone and the like; aldehydes, for example, furfural,crotonaldehyde and the like; butyrolactone, butyrolactam', etc. Y a

v Anti-solvents or diluents may also be employed in the practice of thepresent invention. Thus, diluents such as saturated hydrocarbons,perfluorocarbons, perfiuoroamines, perfiuoroethers, etc. may be added tothe feed stock to be dearomatized or introduced directly into theextraction zone. 7

In the process of the present invention the selective solvent isemployed as aliquid, melt or solution and the feed 747 ff. ment employedforms no part of the present invention sulfur compounds, oxygencompounds and nitrogen compounds. It should be understood that the abovespecific examples of charging stocks which may be refined in accordancewith the present invention are illustrative only and are not intended todelimit the field of applicability of the process of the presentinvention. 1

Other applications of the extraction process of my invention are in theselective extraction of normally gaseous olefins or diolefins from theirmixture with normally gaseous parafiins, for example the selectiveextraction of ethylene from gaseous hydrocarbon streams containingethane and methane, hydrogen, etc., the selective extraction ofpropylene from propylene-containing gasstreams and the like; Myinvention is likewise applicable to the selective extraction ofacetylene from gas mixtures containing the same and methane, hydrogen,ethane, ethylene, etc. By the employment of the extraction or absorptionprocess of the present invention, it is possible to produce normallygaseous unsaturated hydrocarbons of high constocks. Various types ofliquid-liquid extraction operations and suitable extraction equipmentare described, for example, in Chemical Engineers. Handbook (McGraw-Hill Publishing Co., Inc., N. Y., 1950), pp 716 if. and

It should be understood that the specific equipand that any equipmentadaptable for the purposes of contacting the solvent with thehydrocarbon charging stock and thereafter separating an extract phasefrom the refined charging stock can be employed for the purposes of theinvention.

Pyridine oxide exhibits enormous selectivity for the selectiveextraction of gasoline boiling range aromatic total solvent capacity.Both of these characteristics render this solvent extremely attractivefor large scale usage. Coupled with the above-mentioned desirablesolvent characteristics are the further desirable characteristics thatpyridine oxide forms a low viscosity liquid which can be contactedthoroughly with the hydrocarbon and forms a sharp interface duringliquid-liquid extractions.

The following table shows the results of the extraction of a 50 volumepercent n-heptane-SO volume percent toluene feed with pyridine oxide andZ-picoline oxide, re-

spectively. The table also affords a comparison of the efficiency .ofthese solvents with diethylene glycol, which enjoys large commercialusage for the selective extraction of aromatics from naphtha fractionsproduced by catalytic reforming operations. Single-stage extractionswere eliected with amine oxide solventthydrocarbon feed ratio of one at30 C. Diethylene glycol was employed in the] same ratio to feed at 40 C.The ,8 values were calculated from the following equation:

6: molar ratio of toluene/n-heptane in extract phase molar ratio oftoluene/n-heptane in rafiinate phase The symbol ,3 is the so-calledselectivity factor, corresponding to the well known relative volatilityor alpha factor in distillation processes.

The foregoing examples have illustrated specific aspects of myinvention, which is not limited thereto. The extraction process of thepresent invention is readily applicable to the separation of hydrocarbonmixtures and hydrocarbon types not specifically illustrated in theforegoing examples, e. g., the selective separation of olefins fromaromatics, naphthenes from parafiins, naphthenes from aromatics, olefinsfrom saturated hydrocarbons, naphthenes fiorn paraffins, cyclo-olefinsfrom acyclic olefins, mono-olefins from conjugated diolefins, ofconjugated diolefins from non-conjugated diolefins, of diolefins fromaromatics, etc.

Having thus described my process, What I claim is:

1. A process for the selective extraction of an aromatic hydrocarbonfrom a liquid hydrocarbon mixture containing the same and an aliphatichydrocarbon, which process comprises contacting said hydrocarbon mixturewith a solvent selected from the group consisting of pyridine oxide andmonoand poly-alkylpyridine oxides in which the alkyl groups are loweralkyl up to and including butyl in an amount sufiicient at least to forma distinct liquid phase, and separating an extract phase comprising saidsolvent and said aromatic hydrocarbon.

2. A process for the selective extraction of an aromatic hydrocarbonfrom a liquid hydrocarbon mixture containing the same and an aliphatichydrocarbon, which process comprises contacting each volume of saidhydrocarbon mixture in the liquid condition with between about 0.5

and about volumes of a solvent selected from the group consisting ofpyridine oxide and monoand polyalkylpyridine oxides in which the alkylgroups are lower alkyl up to and including butyl at a temperaturebetween about 0 C. and about C., and separating a Iafiinate phase froman extract phase comprising said solvent and said aromatic hydrocarbon.

3. The process of claim 2 wherein said hydrocarbon mixture boils withinthe gasoline boiling range.

4. The process of claim 2 wherein said hydrocarbon mixture comprisesessentially monocyclic aromatic hydrocarbons containing not more than 10carbon atoms per molecule and saturated hydrocarbons.

5. A process for the selective extraction of an aromatic hydrocarbonfrom a naphtha fraction containing the same, which process comprisescontacting said naphtha in the liquid condition with a solvent selectedfrom the group consisting of pyridine oxide and monoandpolyalkylpyridine oxides in which the alkyl groups are lower alkyl up toand including butyl in an amount sufficient at least to form a distinctliquid phase, separating a raflinate phase from an extract phasecomprising said solvent and said aromatic hydrocarbon, and distillingsaid aromatic hydrocarbon from said extract phase.

6. The process of claim 5 wherein the extraction is conducted attemperatures between about 0 C. and about 150 C.

7. The process of claim 5 wherein said solvent is a picoline oxide.

8. A process for the selective extraction of an aromatic hydrocarbonfrom a naphtha fraction containing the same, which process comprisescontacting said naphtha in the liquid condition with pyridine oxide inan amount sufiicient at least to form a distinct liquid phase, andseparating a raflinate phase from an extract phase comprising saidpyridine oxide and said aromatic hydrocarbon.

References Cited in the file of this patent UNITED STATES PATENTS2,516,614 Buis July 25, 1950 FOREIGN PATENTS 472,767 Great Britain Sept.30, 1937

1. A PROCESS FOR THE SELECTIVE EXTRACTION OF AN AROMATIC HYDROCARBONFROM A LIQUID HYDROCARBON MIXTURE CONTAINING THE SAME AND AN ALIPHATICHYDROCARBON, WHICH PROCESS COMPRISES CONTACTING SAID HYDROCARBON MIXTUREWITH A SOLVENT SELECTED FROM THE GROUP CONSISTING OF PYRIDINE OXIDE ANDMONO- AND POLY-ALKYLPYRIDINE OXIDES IN WHICH THE ALKYL GROUPS ARE SLOWERALKYL UP TO AND INCLUDING BUTYL IN AN AMOUNT SUFFICIENT AT LEAST TOSFORM A DISTINCT LIQUID PHASE, AND SEPARATING AN EXTRACT PHASE COMPRISINGSAID SOLVENT AND SAID AROMATIC HYDROCARBON.